It is known for instance from international patent application no. WO 94/06193 to provide a magnetic and fibre material composite cylindrical rotor. WO 94/06193 discloses a composite cylindrical rotor with helically wound tows in a plurality of layers and magnetic material in an epoxy resin in gaps between the tows.
The use of composites can provide a material of relatively high Youngs Modulus (about 120 to 350 GPa compared with about 200 GPa for steel) but with a far lower density (about 1600 kg/m.sup.3 compared with 7800-8000 kg/m.sup.3 for steel). Therefore, for fixed rotor dimensions the stiffness and strength to weight ratios of the composite are 3 to 9 times those of steel. This permits high speeds and faster acceleration.
It is desirable to use such a rotor in eg motors, but so far it has been difficult to achieve the necessary magnetisation distribution, in particular for applications for which multiple poles are desirable.
It is an aim of preferred embodiments of the present invention to overcome or obviate disadvantages encountered with versions of the prior art, whether referred to herein or otherwise.